Github user neggert commented on the issue:
https://github.com/apache/spark/pull/15018
@srowen Addressed your comments and fixed some style issues.
Some updated timings:
Alternating decreasing input
val x = (1 to length).toArray.map(_.toDouble)
val y = x.reverse.zipWithIndex.map{ case (yi, i) => if (i % 2 == 1) yi
- 1.5 else yi}
Before:
| Input Length | Time (us) |
|-------------:|----------:|
| 100 | 1.4 |
| 200 | 3.0 |
| 400 | 101.8 |
| 800 | 2,010,511.7 |
After:
| Input Length | Time (us) |
|-------------:|----------:|
| 100 | 2.5 |
| 200 | 5.8 |
| 400 | 10.1 |
| 800 | 20.7 |
Pathological input from scikit-learn benchmarks:
val y= ((0 until length) ++ (-(length - 1) until length) ++ (-(length -
1) to 0)).toArray.map(_.toDouble)
val x = (1 to y.length).toArray.map(_.toDouble)
Before:
| Input Length | Time (us) |
|-------------:|----------:|
| 40 | 2.2 |
| 80 | 4.7 |
| 160 | 2140.0 |
| 320 | 3,076,508.1 |
After:
| Input Length | Time (us) |
|-------------:|----------:|
| 40 | 5.3 |
| 80 | 10.4 |
| 160 | 21.3 |
| 320 | 41.9 |
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